Why does black hole describe the deconfinement phase?

In the gauge/gravity duality, the deconfinement transition in the gauge theory is identified with the formation of black hole in the dual gravity theory. By assuming this correspondence, many predictions on QGP have been made. In this talk, we justify this approach quantitatively, and also provide an intuitive understanding. Firstly we give quantitative evidence for this identification from the thermodynamic study of the supersymmetric theory. We show that string theory and gauge theory give the same answer, even at finite temperature, including the $1/N$ correction. Then we consider generic gauge theories and show that the deconfinement transition is the condensation of very long and self-intersecting QCD strings, which is analogous to the formation of a black hole in string theory